Abstract-Exploring The Mechanisms Of Sarcoma-Associated Cachexia Cachexia is characterized by weight loss due to the catabolism of skeletal muscle. Over 50% of oncology patients experience cachexia. Cancer-associated cachexia (CAC) correlates with poor performance status and shorter progression-free survival. There are no treatments for CAC. Sarcoma encompasses a diverse group of malignancies that arise from the connective tissues. Virtually nothing is known regarding the mechanisms of sarcoma-associated cachexia (SAC). This represents a significant unmet need. The greatest obstacle in the treatment of SAC is the lack of studies and models that investigate its biology and potential therapeutic solutions. We have observed SAC in our mouse model of osteosarcoma. The cachexia-associated cytokine tumor necrosis factor-? (TNF-?) is overexpressed by the tumors and muscles of sarcoma-bearing mice. Notch3 and its downstream targets are also overexpressed in the tumors and muscles of mice with osteosarcoma. When co-cultured with muscle-derived stem cells (MDSCs), osteosarcoma cells inhibit MDSC differentiation, which is rescued with Notch inhibition. These data suggest novel strategies for the study of SAC and potential solutions. The University of Pittsburgh Musculoskeletal Oncology Tumor Registry and Tissue Bank facilitates the collection of sarcoma patients' clinical data and tissues. SAC is clinically detectable in many sarcoma patients within our registry. We hypothesize that the TNF-? and Notch pathways are important to the biology of SAC, muscle differentiation can be rescued with targeted inhibition of these pathways, and SAC can be investigated with patient-derived sarcoma cells lines. To test these hypotheses, we propose the following: Specific Aim 1: Investigate correlations between human sarcoma cell line gene expression, protein production, and MDSC suppression with the clinical incidence of SAC. We will evaluate human sarcoma cell lines to determine if correlations exist between clinical SAC and the sarcoma cells' gene expressions, protein expressions, and abilities to inhibit MDSC differentiation. Specific Aim 2: Determine if the manipulation of specific factors or pathways causes an alteration in the ability of sarcoma cell lines to suppress myogenesis. We will employ the TNF-? inhibitor etanercept and the Notch inhibitor MK-0752 to determine if the suppression of MDSC differentiation can be rescued with one or both of these agents. We will also evaluate their ability to alter gene expression and protein production. Specific Aim 3: Use tumor xenografts to evaluate the ability of patient-derived sarcoma cell lines to induce SAC, and test the efficacy of TNF-? and Notch inhibition to reverse the cachectic phenotype. We will generate tumor xenografts from human sarcoma cell lines and test their capacities to induce SAC, and the ability of TNF-? and Notch inhibition to rescue the cachectic phenotype in vivo. These experiments will bring understanding to this ubiquitous yet poorly understood aspect of cancer.